Substantial savings of time and money have been realized in the industry by handling a plurality of printed circuit boards (PCB's) while they are still interconnected in a panel of substrate material. With use of interconnected PCB's, processing of such interconnected boards (e.g., populating the PCB's with components, wave soldering of the populated boards, quality control testing such as electrical function testing of whole boards or selected components, and/or encapsulating components populating interconnected PCB's) is more easily enabled. Particularly, such processing of interconnected PCB's is considered very advantageous in the automated processing demands of the electronics industry.
Methods presently used to separate, i.e., singulate, each separate or individual PCB from the interconnected PCB's in the panel of substrate material have typically included shearing, routing, break-away methods of routed tabs, scoring, perforation, and various punch and die techniques.
For example, routing may be performed to route slots in the panel around individual PCB's to define the perimeter of the individual boards. Typically, such routing leaves spaced support tabs around the perimeter for holding the individual boards in place. Such tabs are then cut, broken, or routed to singulate individual boards. Further, for example, scoring has been used for grooving lines along at least portions of individual board perimeters. Such score lines are then used to effect board separation by breaking along the score lines. In addition, various perforations have been used to define the perimeters of the individual boards. Breaking along the lines of perforation are then used for singulation of the individual boards. Punch and die methods of singulation have also been used wherein a custom made die is used to punch each individual board out of the substrate panel and then pulled back into the panel such that after the individual board is populated with components, the boards can be pushed from the panel. Punch and die methods have also been used to remove routed tabs.
The above methods, and various others, have many associated problems. For example, methods of preparing panels for subsequent break-away separation of the PCB's populated with components inherently rob the panel of its rigidity. Consequently, the panels are prone to sagging during wave soldering, excessive warping, and premature breakage prior to subsequent separation into the individual circuit boards. Perforation and scoring yield very poor quality edges. As such, such edges cannot be held to close tolerances. Further, punch and die methods require expensive tooling and cannot be used to process configurations of panels without scrap strips between adjacent individual circuit boards. Further, premature separation during handling of the interconnected circuit boards may occur with a number of the above singulation methods.
Although routing provides an advantageous singulation method, routing also has particular problems or disadvantages associated therewith. For example, excessive treatment by a router can be very expensive, particularly due to the cost of router bits and the time necessary to perform the routing process. For example, routing typically must be performed around the entire perimeter of the interconnected individual circuit boards, or at least along two or more axes (x, y). In addition, although tabs may be utilized to hold the individual circuit boards in place in the interconnected panel of substrate material, the tabs are typically along two different axes of the individual circuit board, requiring the routing tool to be used along at least two different axes to singulate the individual circuit boards. Further, routing of tabs may still result in remaining tab stubs which may require a secondary procedure for removing such stubs from the individual circuit boards.
Various references describe singulation systems. For example, U.S. Pat. No. 4,791,721 describes a singulation system where individual portions of PCB's are interconnected by small break-away tabs so that the individual circuit boards populated with components can be separated without damaging the components assembled on a board. This singulation system uses a punch technique where a punch or die comes into contact with the printed circuit board and punches out the interconnecting portions, i.e., tabs. Other systems use a combination of routing and shearing such as described in U.S. Pat. No. 4,742,615.
Although there are various conventional methods utilized for singulation of interconnected PCB's, there is a need in the art for other advantageous methods for performing such singulation. Further, there is a need for substrates for utilization with such methods which provide such advantages. The present invention provides a singulation method and substrate for use in singulation methods which overcome the disadvantages described above along with other problems as will be apparent from the description below.